The wheels on annie's bicycle are $20$ inches in diameter. if each wheel makes $3$ full revolutions every second, then how many feet does annie travel in $1$ second? give your answer as an integer, rounded to the nearest foot.

We have that
diameter=20 in> r=d/2> 20/2> r=10 in
[length of a circumference]=2*pi*r> 2*pi*10> 20*pi in

we know that
 1 revolution> 20*pi in
3 revolutions (one second)> X
X=3*20*pi> X=60*pi in  ( this is in one second)

1 foot> is equal to 12 in
X> 60*pi in
X=60*pi/12> 5*pi ft> 15.708 ft> 16 ft (in one second)

the answer is
16 ft/sec